Three-phase-current generators are, for example, used in vehicles where they serve to charge a vehicle battery that supplies electrical loads in the vehicle. In a vehicle, such a generator is driven by the vehicle engine. Generators that are used to charge a vehicle battery are also known as alternators.
The output power provided by a generator is dependent on the load of the generator, i.e., it is dependent on the current consumption of a load connected to the generator, and is furthermore dependent on the rotational speed at which the generator is driven. Since both of these influencing variables may vary, the output power of a generator is controllable. The output power may be controlled by controlling a current flowing through the field winding of the generator.